1. Field of the Invention
One aspect of the present invention relates to a signal bandwidth expanding apparatus which converts a signal, such as voice, music, or audio with limited bandwidth, into a wideband signal.
2. Description of the Related Art
When the bandwidth of the signal (input signal) such as voice, music, or an audio is expanded to a wideband signal, in order for the sound to be heard not artificially but naturally, there is a need to properly change a signal processing method of expanding a bandwidth according to a signal (target signal) of which the bandwidth is intended to be expanded and is included in the input signals. As a bandwidth expansion processing method according to the target signal, there a scheme in which the frequency band is expanded after performing a linear prediction analysis on the voice when the target signal is the voice, a scheme in which the frequency band is expanded after performing a frequency domain conversion on the music or the audio when the target signal is the music or the audio, and a scheme in which the frequency band to be expanded is switched based on whether or not the voice is a voiced sound or an unvoiced sound even when the target signal is the voice. In addition, when the above-mentioned bandwidth expanding processes are performed, heavy computational load is needed. However, there is a method of changing the bandwidth expanding method according to a state of a system load (see JP-A-2006-259349, for instance).
In the related signal bandwidth expanding apparatus, the expanding method is changed according to the state of the system load, so that it is possible to prevent the overload of the amount of throughput. However, the frequency balance between the expanded bandwidth and the existing bandwidth is not considered. For this reason, when a part of the bandwidth is expanded, the entire balance of the frequency is broken, so that bandwidth sensitivity of the existing bandwidth is relatively reduced and the high voice quality cannot be felt.